Process and equipment for operating electric arc furnaces

ABSTRACT

A process and apparatus are provided for operating three-phase electric arc furnaces by maintaining equal impedance in all of the three electrode circuits. This may be accomplished by adjusting the relative sag of the circuit wires.

United States Patent l I UN Inventor Mlnlred Jellinghans Rheinhluaen,Germany Appl. No. 861,059

Filed Sept. 25, 1969 Patented July 20, l97l Assignee Heppenshll CompanyPittsburgh, Pa.

PROCESS AND EQUIPMENT FOR OPERATING ELECTRIC ARC FURNACES 5 Claims, 2Drawing Figs.

US. Cl 13/13 Int. CL "05h 7/10 Field Search l3/9, l2,

[56] References Cited UNITED STATES PATENTS 3,078,325 2/1963 Dillon eta]. [3/9 3,156.754 ll/l964 Duchting it 4. 13/9 Primary Examiner-BernardA Gilheany Assistant Examiner-R. N. Envall, Jr. Attorney-Rue", Blenko &Ziesenheim ABSTRACT: A process and apparatus are provided for operatingthree-phase electric arc furnaces by maintaining equal impedance in allof the three electrode circuits. This may be accomplished by adjustingthe relative sag of the circuit wires.

PATENTED JUL20 1971 SHEET 2 OF 2 Fig.2.

mvsmon Manfred Jellinghuus PROCESS AND EQUIPMENT FOR OPERATING ELECTRICARC FURNACES This invention relates to methods and apparatus foroperating electric arc furnaces and particularly to a process andequipment for operating electric arc furnaces on three-phase current forthe production of steel.

In the case of known electric arc furnaces which can be tilted for theproduction of steel, the electric circuits for three electrodes whichare arranged in a triangle are at one side of the furnace. Due to thisarrangement, the circuits have different impedances which cause anirregular burning of the electrodes and the masonry of the furnace.Moreover, in operation, the circuits are changed in position due to theauto matic adjustment of the electrodes as a function of their burning.This also results in a change in the impedances.

In order to reduce this irregular wear which is caused by the variableimpedances and which is called the sharp phase, the suggestion hasalready been made that the arc outputs of the individual electrodes beadjusted diITerently. In the case of another suggestion for reducing theirregular wear, three single-phase transformers which are placed next toeach other are used. However, satisfactory results have not beenobtained with either of these known devices.

Satisfactory results with respect to the uniform burning of theelectrodes and the masonry of the furnaces have been obtained only withnontippable electric arc furnaces which are not used for ferrous alloysand which have single-phase transformers placed in a triangle around thefurnaces. However, such an arrangement is not suitable for electric arcfurnaces which are to be used to produce steel, since the single phasetransformers prevent or even make impossible the tipping of the furnacesdue to their triangular arrangement around the furnace.

Consequently, it is a purpose of the present invention to create aprocess and a device for the operation of threephase fed electric arcfurnaces with which a uniform burning of the electrodes and a uniformwearing of the masonry of the electric arc furnaces can be obtained. Theelectric arc furnaces are to be usable especially for the production ofsteel.

This problem is solved according to the present invention by keeping thecircuit impedances of the electrodes equal to each other. Hereby auniform wear, both of the electrodes as well as the masonry of theelectric arc furnace is assured. Since, for example, the transformer forthe balancing of the three circuit impedance: does not need to bearranged around the furnace, the electric arc furnace can be tippedwithout hindrance by the transformer or circuits and thus can be usedfor the production of steel.

One advantageous embodiment of the present invention provides that theadjustment of the circuit impedances takes place by shifting the circuitcables. This is a very simple possibility of changing the impedances.According to another embodiment of the invention it is preferable thatall the circuits are not changed but that the shifting of the circuitstakes place only at the slack of the circuits.

The process according to the invention is suitable for electric arefurnaces with a random arrangement of electrodes. However, theelectrodes are preferably arranged in a triangle for one furnace andmoreover two of the electrodes are preferably placed at the samedistance from the transformer. Then it is advantageous to undertake theshifting either at the circuits of the center electrode or at bothcircuits of the two outer electrodes. Undertaking the shift at the twoouter circuits has proved particularly advantageous.

A device according to the invention for executing the process ischaracterized by the fact that each electrode is connected with ameasuring apparatus for the circuit: impedance which is connected to acomparison instrument for measuring values of the circuits impedancesandby the fact that at least one adjusting organ for shifting t8e circuitis actuated by the output signals of the comparison instrument.Preferably, an

adjusting organ is provided at both of the outer circuits. However it isalso possible to connect adjusting organs to all circuits so that thecompensation of the circuitss impedanccs can be undertaken at allcircuits.

As a preferred device, the invention suggests that the adjusting organsbe home by position support arms and have lifting and lowering devicesto which the circuits are connected. lnsofar as tubes which direct thecircuits over the electrode support arms have a flexible piece, thecontact point of the lifting and lowering devices according to theinvention should be at the end of the electrode support arm seen fromthe electrode out. By means of the lifting and lowering devices whichare arranged with the electrode carrier arms, changes in the circuitimpedances, which are also influenced to a large extent by the positionof the electrode support arms with respect to each other, can beequalized by lifting and lowering the sag of the circuits.

In the foregoing general description certain objects, purposes andadvantages of this invention have been set out.

Other objects, purposes and advantages will be apparent from aconsideration of the following description and the accompanying drawingsin which:

FIG. 1 is a side elevational view, partly in section, of an apparatusaccording to the invention; and

FIG. 2 is a schematic view of an apparatus such as that of FIG. I with asecond embodiment of control.

Referring to the drawings l have illustrated an electric arc furnace 10having three electrodes ll, 12 and I3, which are arranged in anequilateral triangle. Two of these electrodes II and I3 are placedequally distant from a transformer 14 which is housed within a walledarea 15 having an opening I6 through which the connecting leads [7, I8and 19 pass to the electrodes. Each of the electrodes 11, I2 and I3 ismounted on an adjustable electrode support arm 20, 21 and 22respectively. The electrodes II, 12 and I3 are connected to thetransformer leads 17, I8 and I9 by circuits 23, 24 and 25 respectively.Each of the circuits 23, 24 and 25 passes over the support arms 20, 2tand 22 respectively within pipes 26, 27 and 28 supported on said arms.Each of the outside pipes 26 and 28 have a flexible portion 29 and 30. Alift and lower mechanism 31 and 32 is mounted on each of the outsidesupport arms 20 and 22 and carries the outside pipes 26 and 28. Each ofthe circuits 23, 24 and 25 in the area between the end of pipes 26, 27and 28 and the transformer lead ins I7, I8 and 19 is suspended in theform of a U whose position is changed by lifting or lowering pipes 26and 28 by means of lift and lower mechanisms 3I and 32.

The apparatus works in the following manner. The sag in each of the twooutside circuits 23 and 25 is adjusted by lifting or lowering the pipes26 and 28 by means of lift and lower mechanism 31 and 32. The lift andlower mechanism is controlled as a function of inductance. The controlas shown in FIG. I consists in measuring the position of the individualsupports arms relative to one another by means of depth indicators 33,34 and 35 and slide rheostats 36, 37 and 38 attached thereto andcomparing the two outer electrodes II and I3 with the center electrode12. If a deviation from the normal position is found, the current pathof the electrode in question is either raised or lowered by raising orlowering the pipe 26 or 28 as the case may be to produce impedances inall circuits which are equal. If an irregular burning should occur atthe electrodes 11, I2 or 13 during operation of the furnace, then theelectrodes are adjusted as usual and the circuit impedances consequentlyassume different values which are corrected by the signal from thecomparison measuring devices which signal the lift and lower mechanism31 and 32 through polarized relays 39 and 40 which change the sag in thecircuits in such a way that the impedances become equal in all circuits.

The apparatus shown in FIG. 2 is similar to that of FIG. I in havingelectrodes Ila, 12a and 13a and a transformer 14a spaced therefrom andconnected to the electrodes through circuits 23a, 24a and 250. In thiscase, however, the position of the electrodes is determined by therelative phase position of the electrode. Here the phase position of thetwo outer phases is compared with that of the center or inside phase,When the cos it; of an outer phase deviates from that oftlie insidephase, this is detected by the phase measuring instru ments 4], 41a, 42,42a; 43, 43a which signals the comparison instrument 50 made up ofcomparator 4 1, 45, 4b which signals the motor controllers 48 and 49 sothat the adjusting device 310 and 320 are caused to change the sag inthe corresponding circuit to restore phase coincidence.

In the foregoing specification certain preferred practices andembodiments of this invention have been set forth, how ever, it will beclear to men skilled in the art that the invention may be otherwisepracticed lclaim:

l. A process for operating threephase electric arc furnaces having threeelectrodes, comprising the steps of connecting the three electrodes to apower source through three indepen dent lines each with a cable having anormal sag therein, moni' toring the impedance in each line andadjusting the relative sag in said cables as their impedance changes tomaintain equal impedance in all of the electrode circuits 2v A processas claimed in claim I wherein equal impedance is achieved by arrangingthree electrodes, one for each phase, in a triangle with two of saidelectrodes equidistant from a common power source, monitoring theimpedance of all three lines and automatically changing the relative sagol' the cables connecting said two electrodes and the power source withrespect to cables connecting the third electrode and said power source.

3 An apparatus for operating three-phase electric arc fur naces havingthree electrodes and a transformer spaced therefrom comprising cableconnections between said trans- Former and each of said electrodeshaving a sag therein and forming with said electrodes three separateelectrode circuits, means for measuring the impedance in each saidelectrode circuit and impedance a'djusting means acting on the cable sagin each circuit to alter said cable sag and thereby maintain equalimpedance therein.

4. An apparatus for operating three'phase electric arc fur naccs havingthree electrodes and a transformer spaced therefrom comprisingconnections between said transformer and each of said electrodes formingwith said electrodes, three separate electrode circuits, means formeasuring the impedance in each said electrode circuit, said electrodesbeing carried on electrode arms overhanging the furnace and theelectrode circuit including an elongated pipe carried on lift meansresponsive to impedance change mounted on the support arms and carryinga current wire connected to the trans former, said circuit wire having asag therein adjusted by raising and lowering said elongated pipesrelative to one another 5. An apparatus for operating thrcwphaseelectric arc furnae-es having three electrodes and a transformer spacedtherefrom comprising connections between said transformer and each ofsaid electrodes l'orming with said electrodes, three separate electrodecircuits, means for measuring the impedance in each said electrodecircuit and impedance-adjust mg means acting on each circuit to altersaid circuits to maintain equal impedance therein, said impedancemeasuring means including means for measuring the effective length ofeach electrode and means for controlling the impedance adjusting meansrelative to the effective electrode length.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3,591A86 Dated July 20, 1971 Inventor) Manfred Jellinghaus It is certifiedthat error appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 1, line 7 4, "t8e" should read the Column 2, line 3, "circuits's"should read circuit a line 6, "position" should read electrode Column 3,line 8, before "31a" insert motors Signed and sealed this 10th day ofOctober 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissionerof Patents A po'wso USCOMM-DC scan-Pee 9 Hrs, GOVERNMENT PRINTING OFFICEI'll OSSG'J.I,

1. A process for operating three-phase electric arc furnaces havingthree electrodes, comprising the steps of connecting the threeelectrodes to a power source through three independent lines each with acable having a normal sag therein, monitoring the impedance in each lineand adjusting the relative sag in said cables as their impedance changesto maintain equal impedance in all of the electrode circuits.
 2. Aprocess as claimed in claim 1 wherein equal impedance is achieved byarranging three electrodes, one for each phase, in a triangle with twoof said electrodes equidistant from a common power source, monitoringthe impedance of all three lines and automatically changing the relativesag of the cables connecting said two electrodes and the power sourcewith respect to cables connecting the third electrode and said powersource.
 3. An apparatus for operating three-phase electric arc furnaceshaving three electrodes and a transformer spaced therefrom comprisingcable connections between said transformer and each of said electrodeshaving a sag therein and forming with said electrodes three separateelectrode circuits, means for measuring the impedance in each saidelectrode circuit and impedance-adjusting means acting on the cable sagin each circuit to alter said cable sag and thereby maintain equalimpedance therein.
 4. An apparatus for operating three-phase electricarc furnaces having three electrodes and a transformer spaced therefromcomprising connections between said transformer and each of saidelectrodes forming with said electrodes, three separate electrodecircuits, means for measuring the impedance in each said electrodecircuit, said electrodes being carried on electrode arms overhanging thefurnace and the electrode circuit including an elongated pipe carried onlift means responsive to impedance change mounted on the support armsand carrying a current wire connected to the transformer, said circuitwire having a sag therein adjusted by raising and lowering saidelongated pipes relative to one another.
 5. An apparatus for operatingthree-phase electric arc furnaces haVing three electrodes and atransformer spaced therefrom comprising connections between saidtransformer and each of said electrodes forming with said electrodes,three separate electrode circuits, means for measuring the impedance ineach said electrode circuit and impedance-adjusting means acting on eachcircuit to alter said circuits to maintain equal impedance therein, saidimpedance measuring means including means for measuring the effectivelength of each electrode and means for controlling the impedanceadjusting means relative to the effective electrode length.